This invention relates general to pneumatic radial tires and more specifically to chafer fabric for such tires to prevent abrasion of the tire with the wheel rim flanges when mounting and dismounting such tires.
Automotive tires as traditionally constructed employ as a carcass a polymeric material, such as robber, reinforced with textile cords and steel belts. The wheel engaging portion of the tire is further reinforced by circumferentially extending cores of wire or other relatively rigid material known as "beads". Extending at least partially about these beads and on their surface are "chafer strips" which are intended to resist abrasion of the tire by the rim flanges when the tire is mounted and dismounted.
Chafer fabric is conventionally prepared by flat weaving a fabric, wick-proofing and then friction calendering green robber to both faces of the flat woven fabric and then bias cutting and slitting the calendered fabric into strips of from 1 to 5 inches in width. The step of friction calendering green rubber to the woven fabric and/or skim calendering is carried out to facilitate the ease of bias cutting and piece lay up in green tire building, as well as promoting the vulcanization of the components making up the tire body in the final product.
It should be understood that the chafer fabric of this invention is a woven chafer fabric, that is to say a fabric having substantially straight warp and filling threads interlaced at substantially right angles. A woven fabric should not be confused with a braided or plaited fabric wherein individual threads are skewed and are intertwined at acute angles with each other. Plaited fabrics are not useful as chafer fabrics due to a lack of dimensional stability of the fabric structure.
It is therefore an object of the invention to provide a chafer fabric for tires which can be readily wick-proofed, calendered and molded.
Historically chafer fabrics have been produced out of cotton, but with the advent of the tubeless tire, the yarns in the chafer fabric had to prevent the high pressure air inside the tire from wicking (bleeding) along inside the yarn bundles and reaching outside the rim. If the air can reach the outside tire surface, the tire will slowly lose pressure and gradually go flat. Therefore a wick-proof fabric is essential in the preparation of tires of the tubeless type, and especially high pressure tubeless tires.
For purposes of this invention, the term "wick-proofing" may be defined as a process wherein each cord of a fabric sheet is made impervious to the passage of air. In tubeless tires, high air pressure in the air cavity pushes against the inner surface, and significantly at the bead area, and if the fabric in the chafer is not impervious to the passage of air, air will penetrate the individual cords which then serve as conduits to wick air into the tire body causing blistering and delamination of rubber or leading to the outside atmosphere thereby reducing the internal load supporting air pressure of the tire with undesirable results. Any of a wide variety of wick-proofing processes are satisfactory for use in conjunction with this invention, such as, for instance, wick-proofing processes of the type set forth in U.S. Pat. No. 2,978,784.
In conjunction with tubeless tires, rayon, nylon, and polyester continuous filament yarns became available, and these fibers required an adhesive finish which would adhere to the rubber of the tire. With multifilament yarns bundles this finish (generally referred to as RFL) can penetrate to the core of the yarn bundles (if proper procedures are followed) and block the passage of air. Monofilament yarns, typically nylon, are wick-proof by their nature, and only a small amount of RFL adhesive is needed for adhesion to the rubber.
Monofilament yarns (typically T-6 or T-66 nylon) are widely used around the world because of the guaranteed wick-proof characteristic. However, the monofilament yarn size must be kept small (380-440 denier) to keep it flexible, and therefore it is weak in tensile strength. For the woven fabric to be strong enough to withstand the tension applied during the tire industry's rubber calendering process, the warp construction must be kept relatively high, typically 22-25 ends/inch. Since chafer fabrics are generally used after being cut on the bias, the pick count is typically the same as the warp end count, 22-25.
The use of higher tensile, larger denier multifilament yarns ranging in size from 840-1260 denier, with the most common sizes being 840 and 1000 denier, is possible due to the flexibility provided by the many finer filaments these larger yarn bundles are comprised of. These yarns are either twisted or textured for processability through the textile manufacturing processes. Due to the higher strength, constructions in the range of 12 ends and picks to as high as 18 ends and picks are used. An inherent need of these multifilament yarns is to be impregnated to the core of the yarn bundle with RFL to make them wick-proof. To reliably accomplish this, dip pick-up levels range from 14% to as high as 35%. Monofilament yarn dip pickup, on the other hand, ranges from 3% to 9% which only has to impart satisfactory adhesion--not wick-proofness.
It is another objective of this invention to combine multifilament and monofilament yarns in one chafer fabric to optimize utilization of their physical properties while incurring minimum cost in the fabric. By using multifilament yarn in the warp, either twisted or textured, and monofilament in the filling, warp tensile strength can be maintained at an adequate minimum level, 160 lb.fin. (grab method) while using a low end count (12-18 ends/in.). Since filling direction tensile is not critical to processing or performance in the tire, the monofilament yarn can be used in this direction at a possible range of 12-18 picks/in. The dip pick-up in the warp will provide the wick-proof property while still allowing the multifilament yarns remain flexible. The monofilament filling will only pick up enough RFL to provide adhesion, and the lower denier and low pick count will maintain filling direction flexibility.